Various methods have evolved for treating atrial fibrillation (AF) and/or other arrhythmias of the heart and many include the use of ablation techniques. Various types of devices are used for treating heart tissue and forming lesions in selected areas of the heart for this purpose. Early techniques involved open surgery and small incisions in the heart tissue along selected paths designed to disrupt the pathway of disruptive electrical circuits leading to an abnormal sinus rhythm. Since the incisional scars left by this procedure produced a maze-like pattern, the procedure was referred to as the “maze” procedure. Since the early procedures involved open surgery, and heart-lung bypass, the surgery presented the usual risks, long recovery time, and pain. Over time, ablation devices using various forms of energy, such as radiofrequency (RF), cryotherapy, ultrasound, laser, and microwave, have been developed and used in open surgical procedures, and also in less invasive procedures for ablating tissue of the right and left atrial chambers. These ablation techniques form lesions and, ultimately, scar tissue in the heart designed to promote normal heart rhythm in the manner generally as previously performed with incisions.
Catheter ablation techniques typically use relatively low levels of energy that are capable of creating lesions in tissue sufficient to block abnormal electrical pathways within the tissue. For example, treating chronic AF has involved forming numerous lesions in the heart tissue, with the lesions extending completely through the tissue to provide more complete blockage of electrical pathways. Electrophysiologists often create these lesions using the ablating tip portion of an ablation catheter. This will be an electrode in the case of an RF ablation catheter. Such catheters are configured to create spot lesions and, in order for the electrophysiologist to form linear (straight or curved) and/or closed geometric shapes of scar tissue, such as is required for standard maze procedures, the electrophysiologist must make a series of connected spot lesions with the ablation catheter.
Percutaneous treatment is preferred because it may be used on a beating heart and therefore avoids heart-lung bypass and other disadvantages of open surgery. Catheter ablation techniques typically involve mapping the tissue surface of the left atrium with a sensing catheter and other equipment. Electro-anatomic mapping has also been developed which utilizes a GPS system allowing the electrophysiologist to register points on a GPS map. The electrophysiologist ablates tissue and forms lesions in continuous and surrounding patterns, for example, around the pulmonary veins and in other locations. Standard lesion sets include: 1) isolation of the pulmonary veins in the wall of the left atrial chamber or atrium, each being isolated individually or in pairs including isolating the left superior and inferior veins together and isolating the right superior and inferior veins together, 2) a box lesion or four vein isolation in which a closed pattern of lesions is formed around all four of the veins in the atrial chamber, and 3) a pattern of lesions in the atrial wall leading from the box lesion to the mitral valve. Depending on the needs of the patient and the doctor's treatment plan, the lesion patterns may differ.
Catheters have been developed having more complicated designs including, for example, multiple electrodes for forming circular lesions in surrounding relation to the openings of the pulmonary veins in the left atrium. However, these catheters present challenges in use and can present complications and low efficacy as compared to prior techniques.
It would be desirable to provide improved systems, devices and methods for forming the patterns of lesions using an ablation catheter in a percutaneous treatment of the heart designed to promote normal sinus rhythm.